There has recently been tremendous growth in the area of digital electronics. The use of digital signals for transmitting and conveying data accurately for storage, reproduction or rendering has steadily increased with advances in digital technology. This growth has occurred in part because digital signals offer many advantages for certain types of design applications. However, along with this explosive growth in digital electronics, there has been a concomitant growth of competing digital formats, partially due to different design applications tending to different formats and the promotion of different formats by different companies. For the case of a digital input signal for which the designer knows the formatting, e.g., Format X, it can be a straightforward task to design the inputs of a system to receive Format X signals. Generally, the designer would read the specification for Format X and design the system to conform to Format X signals.
However, when the designer is blind to the formatting of the input signal i.e., when the designer does not know whether an input signal will be formatted according to Format X, Format Y, or another format, a difficulty arises with respect to processing the input signal. Format X signals generally can not be processed correctly in a system expecting Format Y signals, and vice versa. For example, two competing digital audio signal formats are the I2S and SPDIF formats. Data in I2S signals are formatted/encoded differently than data in SPDIF signals. Accordingly, the designer presently has to know the format of inputs to such a digital audio system in advance in order to efficiently process the digital audio inputs.
In addressing the above problem of unknown formatting of input signals, it has been proposed that a multiplexer be employed, having a multiplexer select, such that a system outputs one signal according to one multiplexer select voltage (e.g., 5 V), and the system outputs another signal according to another multiplexer select voltage (e.g., 0 V). However, at present, an additional multiplexer select circuit pin is required to accommodate the multiplexer select input. As a result, some external means for correctly setting the select pin according to the input into the system needs to be provided.
Thus, it would be advantageous to provide a circuit having audio input format auto detection capabilities such that a designer could design a circuit that is independent of audio input format. It would be further advantageous to provide such a circuit with a minimum pin count and without an external formatting select pin. The present invention has been developed to meet these needs in the art.